The long term objective of this proposal is to establish Protein Arginine Methyltransferases and Dimethyarginine Dimethylaminohydrolase (DDAH), the enzymes responsible for methylarginine synthesis and metabolism, as a key regulator of endothelial function. It is our hypothesis that the increased plasma ADMA observed in cardiovascular disease is a biomarker of DDAH activity and that many of the endothelial affects attributed to ADMA are directly manifested through altered DDAH-PRMT activity. We have shown that in addition to the direct effects of ADMA on eNOS activity, DDAH modulates endothelial NO production through ADMA independent mechanisms involving altered protein-methylation and amino acid metabolism. The goals of the current proposal are to: 1.) identify the pathways of ADMA metabolism in the endothelium; 2.) determine the mechanisms through which DDAH modulates endothelial protein-arginine methylation and define the effects of protein methylation on endothelial function; 3.) determine the mechanisms through which DDAH regulates endothelial L-arginine metabolism and the consequences on endothelial NO production; and 4.) identify the mechanisms through which the PRMT-DDAH-ADMA axis regulates endothelial function and atherosusceptibility. For each of these aims, a combination of cellular, molecular, biophysical and physiological approaches will be used to characterize the effects of DDAH on endothelial function using in vitro and in vivo models. Results from these studies will provide fundamental mechanistic information regarding the mechanisms through which the PRMT-DDAH-ADMA axis modulates cellular function and may lead to new approaches to treat vascular disease.